JP2013057070A - Cross-linked polyolefinic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cross-linked polyolefinic resin foam excellent in heat resistance, and facilitating secondary processing to a complicated shape.SOLUTION: This cross-linked polyolefinic resin foam comprises a polyolefinic resin composition including: 20-50 wt.% of a polypropylene-based resin (A) at least one of endothermic peaks by the differential scanning calorimeter of which is 160°C or higher; 20-50 wt.% of a polypropylene-based resin (B) at least one of endothermic peaks by the differential scanning calorimeter of which is lower than 160°C; and 20-40 wt.% of polyethylene-based resin (C). The foam is obtained by molding the polyolefinic resin composition into arbitrary shape, and thereafter foaming and cross-linking the resin.

Description

  The present invention relates to a crosslinked polyolefin resin foam having excellent heat resistance and capable of secondary processing into a complicated shape by vacuum molding or compression molding.

  Crosslinked polyolefin-based resin foams are generally excellent in flexibility, lightness, and heat insulation, and have been conventionally used as interior materials for vehicles such as ceilings, doors, and instrument panels. These vehicle interior materials are usually formed into a predetermined shape by secondary processing of a sheet-like crosslinked polyolefin resin foam by vacuum molding, compression molding or the like. Cross-linked polyolefin resin foams are usually made of a polyvinyl chloride resin sheet, a thermoplastic elastomer sheet, a natural cloth or artificial cloth, and a skin material such as leather (other materials). ) Is used as a laminate.

  Recent vacuum molding of cross-linked polyolefin resin foams and compression molding such as stamping molding require deep processing to increase the processing temperature to 120-200 ° C to improve productivity, or to process into a complicated shape. Molding is required. Therefore, the cross-linked polyolefin resin foam is required to have good moldability at high temperatures.

  In order to solve this problem, a method of improving the heat resistance by increasing the melting point of the resin has been proposed (see Patent Document 1). However, with this proposal, the elongation becomes insufficient, and high shear is applied to the extremely sharp part in the molded body, the vertical wall part where the flow rate of the resin that becomes the aggregate becomes high due to stamping molding, etc. There was a case where it was torn at the part.

Japanese Patent No. 3308724

  Accordingly, in view of the background of the above-described conventional technology, an object of the present invention is to provide a crosslinked polyolefin resin foam that has excellent heat resistance, good moldability at high temperatures, and can be secondarily processed into a complicated shape. There is.

  In order to solve the above problems, the present invention employs the following means. That is, the cross-linked polyolefin resin foam of the present invention has 20 to 50% by weight of a polypropylene resin (A) having an endothermic peak of 160 ° C. or more as measured by a differential scanning calorimeter, and an endothermic peak of 160 or more by a differential scanning calorimeter. A cross-linked polyolefin resin foam comprising a polyolefin resin composition containing 20 to 50% by weight of a polypropylene resin (B) at 20 ° C. and 20 to 40% by weight of a polyethylene resin (C).

  According to a preferred embodiment of the crosslinked polyolefin resin foam of the present invention, the polypropylene resin (A) is preferably a group consisting of an ethylene-propylene block copolymer, a homopolypropylene and an ethylene-propylene random copolymer. At least one resin selected from the group consisting of:

  According to a preferred embodiment of the crosslinked polyolefin resin foam of the present invention, the polypropylene resin (A) has a melt flow rate (may be abbreviated as MFR) in the range of 0.4 to 1.8 g / 10 min. And the weight ratio of the polypropylene resin (A) to the polypropylene resin (B) is in the range of 1: 0.5 to 1: 1.5.

  The crosslinked polyolefin resin foam of the present invention can be laminated with other materials such as a skin material to form a laminate.

  The crosslinked polyolefin resin foam of the present invention and the laminate can be formed into a molded body by molding them into an arbitrary shape.

  The crosslinked polyolefin resin foam of the present invention, the laminate or the molded article is suitably used as an automobile interior material.

  According to the present invention, a cross-linked polyolefin system that can be molded into a complicated shape without causing molding defects, has excellent heat resistance, good moldability at high temperatures, and balances moldability and heat resistance. It is possible to obtain a resin foam, in particular, a crosslinked polyolefin resin foam suitably used for stamping molding of automobile interior materials.

It shows that there is a more preferable relationship with respect to the melt flow rate (MFR) of the polypropylene resin (A) used in the present invention and the weight ratio of the polypropylene resin (A) and the polypropylene resin (B). . FIG. 1 is a schematic diagram showing the contents of a problem that may occur in each section of the relationship.

  Specifically, in FIG. 1, when the melt flow rate (MFR) of the polypropylene resin (A) is low, decomposition of the pyrolytic foaming agent is accelerated by applying high shear when kneading the polyolefin resin composition. The aesthetics of the resulting crosslinked polyolefin resin foam may be impaired. In addition, when the MFR of the polypropylene resin (A) is high, a tensile elongation at room temperature sufficient for general molding methods (for example, a stamping molding method and a vacuum molding method) cannot be obtained. Heat resistance when used may not be sufficient. Due to the weight ratio between the polypropylene resin (A) and the polypropylene resin (B), if the polypropylene resin (B) is small, there is a possibility that sufficient tensile elongation at normal temperature cannot be obtained. In addition, even when the amount of the polypropylene resin (B) is large, it is considered that sufficient heat resistance when used in the stamping molding method cannot be obtained.

  In FIG. 1, the MFR of the polypropylene resin (A) is particularly preferably in the range of 0.4 to 1.8 g / 10 min, and the weight ratio of the polypropylene resin (A) to the polypropylene resin (B) is 1: 0. It is illustrated that a range of 5 to 1: 1.5 is particularly preferred.

  The present inventors have intensively investigated the above-mentioned problem, that is, a crosslinked polyolefin resin foam excellent in heat resistance that can be molded into a complicated shape without causing molding defects, and a polypropylene type having a specific melting point peak. A polyolefin resin composition composed of a resin (A), a polypropylene resin (B) having a specific melting point peak, and a polyethylene resin was molded, crosslinked, and foamed. Thus, the present inventors have reached the present invention.

  That is, the cross-linked polyolefin resin foam of the present invention has 20-50% by weight of a polypropylene resin (A) having a heat absorption peak of 160 ° C. or higher of at least one of the endothermic peaks measured by the differential scanning calorimeter, and the endothermic peak measured by the differential scanning calorimeter. It is basically composed of a polyolefin resin composition containing 20 to 50% by weight of a polypropylene resin (B) of less than 160 ° C. and 20 to 40% by weight of a polyethylene resin (C).

  Examples of the polypropylene resin (A) used in the present invention include resins typified by an ethylene-propylene random copolymer, an ethylene-propylene block copolymer, an ethylene-propylene random block copolymer, and a homopolypropylene. Among them, an ethylene-propylene block copolymer that is excellent in low-temperature characteristics while maintaining heat resistance to be achieved by the present invention is particularly preferably used.

  Among the copolymers mentioned here, the ethylene content of the ethylene-propylene random copolymer and the ethylene-propylene random block copolymer is less than 1% by weight in relation to the endothermic peak by the differential scanning calorimeter. Is preferred. Further, the content of the ethylene-propylene rubber in the ethylene-propylene block copolymer and the ethylene-propylene random block copolymer is not particularly specified, but is within a range not impairing the effects of the present invention, for example, less than 30% by weight. It is preferable.

  The molecular weight of the polypropylene resin (A) in the present invention may be a general molecular weight and is not particularly defined. For example, the weight average molecular weight is in the range of 100,000 to 1,500,000, and the molecular weight distribution (weight average molecular weight / number average molecular weight) is preferably 1.5 to 10.

  The melt flow rate (MFR) of these polypropylene resins (A) is measured under normal conditions of a temperature of 230 ° C. and a load of 2.16 kgf based on JIS K7210 (1999), and is used in the present invention. The MFR of the polypropylene resin (A) is preferably in the range of 0.4 to 1.8 g / 10 min.

  If this MFR is less than 0.4 g / 10 min, the thermal decomposable foaming agent may be decomposed by shearing during sheeting, which may cause problems in appearance, and if the MFR exceeds 1.8 g / 10 min, foaming will occur. The heat resistance of the sheet may be insufficient. The MFR of the polypropylene resin (A) is more preferably 0.5 to 1.7 g / min, still more preferably 0.6 to 1.6 g / min.

  In general, MFR has a strong correlation with the molecular weight. If the molecular weight is large, the MFR value decreases. Conversely, if the molecular weight is small, the MFR value increases. However, the value varies depending on the copolymerization ratio, molecular weight distribution, etc., and thus cannot be defined unconditionally.

  In the polypropylene resin (A) used in the present invention, it is important that at least one of the endothermic peaks measured by the differential scanning calorimeter is 160 ° C. or higher.

  The endothermic peak here refers to an endothermic reaction that occurs when a crystalline polymer crystal melts, measured by a differential scanning differential calorimeter, and generally treated as a melting point. If this endothermic peak is high, it can be said that the higher the endothermic peak, the more difficult it is to melt and the higher the heat resistance.

  In order for at least one of the endothermic peaks of the polypropylene resin (A) measured by a differential scanning calorimeter to be 160 ° C. or higher, the weight average molecular weight is preferably 100,000 or higher, and an ethylene-propylene random copolymer or ethylene- In a polypropylene resin in which ethylene molecules are introduced into the main chain, such as a propylene random block copolymer, the ethylene content is preferably less than 1% by weight.

  In the crosslinked polyolefin resin foam of the present invention, it is important that the amount of the polypropylene resin (A) is 20 to 50% by weight, and the amount is preferably 25 to 45% by weight, and more preferably. Is 28 to 42% by weight. If the amount of the polypropylene resin (A) is less than 20% by weight, the heat resistance at the time of molding is insufficient, and the surface may be rough due to resin flow, such as at the time of stamping molding. On the other hand, if the amount of the polypropylene resin (A) exceeds 50% by weight, the heat decomposable foaming agent is decomposed during sheet molding, which may cause a problem in appearance.

  It is important that the polypropylene resin (B) used in the present invention has an endothermic peak by a differential scanning calorimeter of less than 160 ° C. The endothermic peak here is synonymous with the endothermic peak for the polypropylene resin (A).

For homopropylene and ethylene-propylene block copolymers, the weight average molecular weight is preferably 100,000 or less, or for ethylene-propylene random copolymers and ethylene-propylene random block copolymers, ethylene is preferred. The content is preferably 1% by weight or more.
Examples of such polypropylene resins (B) used in the present invention include propylene homopolymers such as isotactic homopolypropylene, syndiotactic homopolypropylene and atactic homopolypropylene, ethylene-propylene random copolymers, An α-olefin-propylene copolymer represented by an ethylene-propylene block copolymer and an ethylene-propylene random block copolymer (the α-olefin here is ethylene, 1-butene, 1-pentene, 1 -Hexene, 1-heptene, 1-octene, 1-nonene, etc.), other modified polypropylene resins, and propylene block copolymers having block portions such as ethylene, isoprene, butadiene, and styrene. I can get lost. You may use these 1 type or in mixture of 2 or more types.
As the polypropylene-based resin (B), an ethylene-propylene random copolymer is particularly preferably used in terms of achieving a good balance between moldability and heat resistance.
The MFR of the polypropylene resin (B) is not particularly specified. It may be arbitrarily determined within the range where desired physical properties and manufacturing problems do not occur.

The molecular weight of the polypropylene resin (B) in the present invention may be a general molecular weight and is not particularly defined. For example, a weight average molecular weight in the range of 1,000 to 1,500,000 may be used.
In the crosslinked polyolefin resin foam of the present invention, it is important that the amount of the polypropylene resin (B) having an endothermic peak by the differential scanning calorimeter of less than 160 ° C. is in the range of 20 to 50% by weight, Preferably it is the range of 30-40 weight%. If the amount of the polypropylene resin (B) is more than 50% by weight, there is a problem in heat resistance, and if it is less than 20% by weight, desired moldability cannot be obtained.

Examples of the polyethylene resin (C) used in the present invention include an ethylene homopolymer (ultra low density: less than 0.910 g / cm ³ , low density: 0.910 to 0.925 g / cm ³ , medium density). : 0.926 to 0.940 g / cm ³ , high density: 0.941 to 0.965 g / cm ³ ), a copolymer containing ethylene as a main component, and a mixture thereof. Examples of the ethylene-based copolymer include ethylene and α-olefins having 4 or more carbon atoms (for example, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, etc.) may be mentioned, and an ethylene-α-olefin copolymer (linear low density polyethylene) obtained by polymerization may be used. In the present invention, linear low density polyethylene is particularly preferably used as the polyethylene resin.

  The reason why linear low-density polyethylene is preferable is that, when used, the moldability that the present invention intends to achieve is expected to be improved.

  The molecular weight of the polyethylene resin (C) in the present invention may be a general molecular weight and is not particularly defined. For example, the number average molecular weight may be in the range of 1,000 to 1,000,000.

  The melt flow rate (MFR) of the polyethylene resin (C) is measured under normal conditions of a temperature of 190 ° C. and a load of 2.16 kgf based on JIS K7210 (1999). The melt flow rate (MFR) of the polyethylene resin (C) is preferably in the range of 0.5 to 15 g / 10 min. If the MFR is less than 0.5 g / 10 min, the surface of the sheet may become rough when forming into a sheet, resulting in problems in appearance. If the MFR exceeds 15 g / 10 min, the heat resistance of the foamed sheet May be insufficient. The range of the MFR is more preferably 1.0 to 10 g / 10 min.

  In general, MFR has a strong correlation with the molecular weight. If the molecular weight is large, the MFR value decreases. Conversely, if the molecular weight is small, the MFR value increases. However, the value varies depending on the form and amount of molecular branching, the molecular weight distribution, and the like, so it cannot be defined unconditionally.

  In the crosslinked polyolefin resin foam of the present invention, the addition of the polyethylene resin (C) in accordance with the desired physical properties is taken into consideration in consideration of the balance with the decrease in heat resistance due to the addition of the polyethylene resin (C). The amount can be determined. The specific amount of the polyethylene resin is 20 to 40% by weight, preferably 20 to 35% by weight.

When the addition amount of the polyethylene resin (C) is less than 20% by weight, high shear is applied when the polyolefin resin composition is formed into a sheet shape, and the decomposition of the pyrolytic foaming agent is promoted. When it is made into a foam, the appearance may be impaired, and when it is more than 40% by weight, the heat resistance to be achieved by the present invention may be impaired.
In the crosslinked polyolefin resin foam of the present invention, other thermoplastic resins may be added as long as the characteristics of the present invention are not significantly impaired.
Examples of other thermoplastic resins in the present invention include those that do not contain halogen, such as polystyrene, polymethyl methacrylate, acrylic resins such as styrene-acrylic acid copolymer, styrene-butadiene copolymer, ethylene, and the like. -Vinyl acetate copolymer, polyvinyl acetate, polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methyl cellulose, hydroxymethyl cellulose, cellulose derivatives such as hydroxymethyl cellulose and hydroxypropyl cellulose, saturated alkyl polyester Resin, polyethylene terephthalate and polybutylene terephthalate, aromatic polyester resin such as polyarytate, polyamide resin, polyacetal resin, Polycarbonate resins, polyester sulfone resin, polyphenylene sulfide resin, polyether ketone resin, and a copolymer having a vinyl polymerizable monomer and nitrogen-containing vinyl monomers. Furthermore, other thermoplastic resins include elastomers such as isoprene rubber, styrene butadiene rubber, butyl rubber, dimethyl silicone rubber and ethylene propylene rubber.
Examples of other thermoplastic resins containing halogen include polyvinyl chloride, polyvinylidene chloride, polychloroethylene trifluoride, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, and solvent-soluble perfluorocarbon resin. Can be mentioned. One kind of these resins may be used, or a plurality of kinds of resins may be contained. In accordance with the physical properties desired for the crosslinked polyolefin resin foam of the present invention, the types and addition amounts of other thermoplastic resins are selected.

  The gel referred to in the present invention refers to a cross-linked and polymerized resin, which is a part that is not plasticized at a normal molding temperature, for example, 180 ° C. If this part increases, heat resistance will improve, but moldability will fall. Therefore, this ratio (hereinafter referred to as a gel fraction in the present invention) is arbitrarily selected according to the molding method.

Any value can be selected for the gel fraction of the crosslinked polyolefin resin foam of the present invention by a molding method. For example, the gel fraction of the crosslinked polyolefin resin foam molded by the low pressure injection molding method is preferably 45 to 65%, more preferably 50 to 60%. Moreover, the gel fraction of the crosslinked polyolefin resin foam molded by the vacuum molding method is preferably 25 to 50%, more preferably 30 to 45%. The gel fraction of the crosslinked polyolefin-based resin foam molded by a molding method in which low-pressure injection molding is performed after pre-vacuum molding is preferably 40 to 60%, more preferably 45 to 55%.
The gel fraction referred to in the present invention is a calculated value. Specifically, the gel fraction was obtained by accurately weighing about 50 mg of a crosslinked polyolefin resin foam, immersing it in 25 ml of xylene at a temperature of 120 ° C. for 24 hours, and filtering through a 200 mesh stainless steel wire mesh. The insoluble matter is vacuum-dried. Subsequently, the weight of this insoluble matter is accurately weighed. The gel fraction means a percentage of the weight of this insoluble matter with respect to the weight of the foam before dissolution, and is expressed by the following formula.
Gel fraction (%) = (weight of insoluble matter / weight of foam before dissolution) × 100
In the cross-linked polyolefin resin foam of the present invention, as one index representing moldability, the tensile elongation at room temperature (%) measured based on JIS K6767 (1999) is the apparent density b (kg / kg). It can be used as an index that m ³ ) and the gel fraction c (%) satisfy the relationship in the following formula (1).
a> 2 * b-3 * c + 200 Formula (1)
When the condition of the above formula (1) is not satisfied, particularly when low pressure injection molding or the like is performed, the corner R may be subjected to high shear and may be broken.

In this invention, there exists a more preferable relationship regarding the melt flow rate (MFR) of the polypropylene resin (A) used, and the weight ratio of this polypropylene resin (A) and a polypropylene resin (B). The melt flow rate of the more preferable polypropylene resin (A) is in the range of 0.4 to 1.8 g / 10 min. When the melt flow rate of the polypropylene resin (A) is smaller than 0.4 g / 10 min, as described above, the thermal decomposable foaming agent is decomposed by shearing when forming into a sheet, causing a problem in appearance, and the melt When the flow rate is larger than 1.8 g / 10 min, the heat resistance may be lowered and the tensile elongation may be insufficient.
And the preferable range of the weight ratio of a polypropylene resin (A) and a polypropylene resin (B) is 1: 0.5-1: 1.5. When the polypropylene resin (B) is less than 0.5 in the weight ratio, high shear is applied during kneading, decomposition of the pyrolytic foaming agent may occur, and the surface state may be deteriorated. On the other hand, when the weight of the polypropylene resin (B) is more than 1.5, the resulting crosslinked polyolefin resin foam may have insufficient heat resistance.
The contents of problems that may occur in each section of the relationship shown above are schematically shown in FIG.

  In producing a foam from a polyolefin resin composition containing the polypropylene resin (A), polypropylene resin (B) and polyethylene resin (C) used in the present invention, a pyrolytic foaming agent is preferably used. .

  Any pyrolytic foaming agent may be used as long as it has a decomposition temperature higher than the melting temperature of the polyolefin resin composition. Preferred thermal decomposition type blowing agents include azodicarbonamide, and hydrazosicarbonamide, azodicarboxylic acid barium salt, dinitrosopentaethylenetetramine, nitrosoguanidine having a decomposition temperature equal to or higher than azodicarbonamide. , P, p′-oxybisbenzenesulfonyl semicarbazide, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, barium azodicarboxylate, azobisisobutyronitrile, toluenesulfonyl hydrazide and the like. These pyrolytic foaming agents may be used alone or in combination of two or more. The blending amount of the pyrolytic foaming agent is generally about 2 to 40 parts by weight with respect to 100 parts by weight of the total amount of the resin components, and is set according to a desired foaming ratio.

  Moreover, when manufacturing the crosslinked polyolefin resin foam of this invention, a crosslinking adjuvant can be used.

  In the present invention, a polyfunctional monomer can be used as a crosslinking aid. Examples of the polyfunctional monomer include divinylbenzene, diallylbenzene, divinylnaphthalene, divinylbiphenyl, divinylcarbazole, divinylpyridine, and their nucleus-substituted compounds and related homologues, ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diester. Acrylate, butylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1 , 9-nonanediol diacrylate, 1,9-nonanediol dimethacrylate, 1,10-decandio Diacrylate, and acrylic acid or methacrylic acid compounds such as 1,10-decanediol dimethacrylate, aliphatic divalent carboxylic acids such as divinyl phthalate, diallyl phthalate, diallyl malate and bisacryloyloxyethyl terephthalate or aromatics Divalent carboxylic acid vinyl ester, allyl ester, acryloyloxyalkyl ester, methacryloyloxyalkyl ester, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, polyethylene glycol divinyl ether, hydroquinone divinyl ether and bisphenol A diallyl ether Aliphatic dihydric alcohol or aromatic dihydric alcohol vinyl And monomers such as maleyl compounds such as thiol, allyl ether, N-phenylmaleimide and N, N′-m-phenylenebismaleimide, dipropargyl phthalate, and dipropargyl maleate. be able to.

  Furthermore, in the present invention, as other crosslinking aids, such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tetramethylol methane triacrylate, tetramethylol methane trimethacrylate, tetramethylol methane tetraacrylate and tetramethylol methane tetramethacrylate Acrylic acid-based compounds or methacrylic acid-based compounds, trimellitic acid triallyl ester, pyromellitic acid triallyl ester and pyromellitic acid tetraallyl ester Allyl ester, polyacryloyloxyalkyl ester, polymethacryloyloxyalkyl ester, triallyl cyanurate and triallyl ester Allyl ester of cyanuric acid or isocyanuric acid, such as cyanurate, triallyl phosphate, and the polyfunctional monomers such as Trisacryl oxyethyl phosphate can also be used.

  Said crosslinking adjuvant may be used independently and may mix 2 or more types. The amount of the crosslinking aid is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight with respect to 100 parts by weight of the total amount of the resin components, and a desired gel fraction. Is set according to

  In addition, the polyolefin resin composition can be crosslinked by combining a crosslinking aid and an organic peroxide. As this organic peroxide, for example, methyl ethyl ketone peroxide, t-butyl peroxide, dicumyl peroxide and the like are used. The compounding amount of the organic peroxide is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight with respect to 100 parts by weight of the total amount of the resin components, and the desired gel content. It is set according to the rate.

  In the present invention, the gel fraction is set in consideration of heat resistance and cushioning properties. In the present invention, when the polyolefin resin composition is crosslinked, a so-called chemical crosslinking method and a crosslinking method using ionizing radiation. May be used in combination.

  As long as the characteristics of the present invention are not impaired, the polyolefin-based resin composition includes a foaming agent decomposition accelerator, a cell nucleus modifier, an antioxidant, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and an inorganic filler. Various additives such as an agent can be blended.

  In this invention, after shape | molding the polyolefin resin composition formed by mix | blending each said component in a predetermined shape, it can bridge | crosslink and foam and a crosslinked polyolefin resin foam can be manufactured.

  Specific examples of the method for producing the crosslinked polyolefin resin foam include the following production methods. Using a kneading apparatus such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer, and a mixing roll, a predetermined amount of the polyolefin-based resin composition is uniformly uniform below the decomposition temperature of the pyrolytic foaming agent. It is melt-kneaded and formed into a sheet.

  Then, the obtained sheet-like material is irradiated with a predetermined dose of ionizing radiation to crosslink the resin, and the crosslinked sheet-like material is heated to a temperature higher than the decomposition temperature of the thermally decomposable foaming agent to be foamed. As the ionizing radiation, electron beams, X-rays, β rays, γ rays and the like are used. The irradiation dose is generally about 1 to 300 kGy, and the dose is set according to a desired gel fraction. Further, instead of crosslinking by ionizing radiation irradiation, peroxide crosslinking or silane crosslinking may be performed.

The foamable sheet material in which the resin is crosslinked is, for example, hot air, infrared rays, metal bath, oil bath, salt bath, etc., at a temperature not lower than the decomposition temperature of the pyrolytic foaming agent and not lower than the melting point of the resin, for example, Heating to a temperature of 190 to 290 ° C., the resin is foamed by the decomposition gas of the foaming agent, and the crosslinked polyolefin resin foam of the present invention is obtained.
It is preferable that the endothermic peak of the crosslinked polyolefin resin foam thus obtained by a differential scanning calorimeter is 155 ° C. or higher. The reason for this is in particular, the melting of the foam at the gate part (gate mark) for injecting the molten resin generated during low-pressure injection molding, the melting of the foam (avatar) caused by high shear on the vertical wall, etc. This is because it can be expected that the amount of appearance defects will be reduced as compared with the case where the appearance defects are not satisfied.

  In this manner, a crosslinked polyolefin resin foam having independent bubbles, optionally exhibiting a foaming ratio in the range of 2 to 45 times depending on the amount of foaming agent, and having a beautiful appearance is obtained.

As a method for evaluating the heat resistance of the crosslinked polyolefin resin foam of the present invention, the tensile elongation characteristics at high temperatures can be used as one index. As heat resistance, it is preferable that the relationship of the following formula (2) is established between the tensile elongation (%) at 150 ° C. and the tensile elongation (%) at 170 ° C.
(Tensile elongation at 170 ° C.) / (Tensile elongation at 150 ° C.) ≧ 1 Formula (2)
When the relationship of the formula (2) is not satisfied, it is expected that deterioration with respect to heating is promoted, and there is a possibility of causing a problem during high temperature molding.

  In addition, as an evaluation of the moldability of the crosslinked polyolefin resin foam of the present invention, the molding drawing ratio can be used as an index. An arbitrary value may be selected for the molding drawing ratio by a molding method. For example, the molding drawing ratio of the crosslinked polyolefin resin foam obtained by the low-pressure injection molding method is preferably 0.4 or more, more preferably 0.5 or more. Moreover, in the case of a vacuum forming method, 0.6 or more is preferable, More preferably, it is 0.7 or more. In the case of a molding method in which low-pressure injection molding is performed after pre-vacuum molding, 0.5 or more is preferable, and 0.6 or more is more preferable.

  Moreover, the laminated body which shows the heat resistance more excellent with respect to the heating at the time of shaping | molding can be obtained using the crosslinked polyolefin resin foam obtained by the method described so far. The laminate can be produced by laminating and pasting other materials on the crosslinked polyolefin resin foam by a conventionally known method.

  Other materials to be laminated on the cross-linked polyolefin resin foam of the present invention include fabric-like materials using natural fibers and artificial fibers, sheet-like materials made of polyvinyl chloride resin, and sheet-like materials made of thermoplastic olefin (TPO). , Thermoplastic elastomer sheet materials, skin materials such as leather, nonwoven fabrics using thermoplastic resin fibers, polyolefin resin non-crosslinked foam sheet materials, for example, open-cell foams using polyurethane, polyester films and polyacrylic Examples include at least one selected from known films such as films represented by films and the like, cardboard plastic, foamed paper, and metal layers represented by copper, silver and nickel. In the present invention, a plurality of these other materials may be laminated, or may be laminated on both the front and back surfaces of the crosslinked polyolefin resin foam, or two or more kinds may be combined.

As a method for bonding the crosslinked polyolefin resin foam of the present invention and the above-mentioned other materials, for example, an extrusion laminating method for melting a thermoplastic resin, an adhesive laminating method for pasting after applying an adhesive, a skin material, etc. are necessary. Then, a heat-lamination method (also referred to as fusion), a hot melt method, a high-frequency welder method, and a metal, etc. include electroless plating method, electrolytic plating method, and vapor deposition method. However, it is not limited to these, and both may be bonded by any method.
The crosslinked polyolefin resin foam or laminate obtained by the methods described so far can be molded into a desired shape by molding them into an arbitrary shape. Examples of the molding method include high pressure injection molding, low pressure injection molding, male drawing vacuum molding, female drawing vacuum molding and compression molding.

In the above molding method, a thermoplastic resin is usually used as a base material. The base material referred to in the present invention is a skeleton of the molded body, and the shape thereof is selected according to the shape of a desired molded body such as a plate shape or a rod shape.
As the thermoplastic resin for the substrate used in the present invention, polypropylene resin, propylene and α-olefin (the α-olefin is ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-heptene). Octene, etc.) are random, random / block or block copolymerized polypropylene resin, polyethylene resin, copolymer resin of ethylene and α-olefin, copolymer resin of vinyl acetate or acrylate ester, A polyolefin resin, ABS resin, polystyrene resin, or the like in which these are arbitrarily mixed can be applied.
If a resin having a considerably high melting point such as a polyamide resin or a polybutylene terephthalate resin is used for the base material for the cross-linked polyolefin resin foam, the melting temperature of the base material layer becomes high. Depending on the temperature, there may be a disadvantage that bubbles of the crosslinked polyolefin resin foam are destroyed during pressure molding. Therefore, it is necessary to select the resin for the base material layer in consideration of a molding method and the like.

  In the present invention, the base material layer is used to distinguish the base material and the cross-linked polyolefin resin foam or the laminated skin material from the point of being laminated at the time of molding. .

  The present invention makes it possible to obtain automotive interior materials such as ceilings, doors, and instrument panels using the crosslinked polyolefin resin foam or laminate or molded product obtained by the method described so far. . It is expected that the defective rate is reduced by exhibiting excellent heat resistance against processing during molding, for example, heating in low-pressure injection molding.

  In the present invention, each physical property was measured and evaluated by the following methods.

(Measuring method of melt flow rate)
According to JIS K7210 (1999) “Plastics—Test methods for melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics”. Based on Annex B (reference) “Standards and designation of thermoplastic materials and test conditions” for the above standards, polypropylene resin (A) has a temperature of 230 ° C., a load of 2.16 kgf, and a polyethylene resin has a temperature of 190 ° C., a load. The test was performed under the condition of 2.16 kgf. The melt flow rate in the present invention is obtained by measuring the weight of the resin coming out of the die for 10 minutes using a melt indexer model F-B01 manufactured by Toyo Seiki Seisakusho Co., Ltd. Say things.

(Analysis method of endothermic peak by differential scanning calorimeter)
The analysis of the endothermic peak by the differential scanning calorimeter in the present invention was performed by the following method. About 10 mg of a polyolefin resin (polypropylene resin, polyethylene resin, or the like in the present invention) or a foam of a crosslinked polyolefin resin foam, which is crushed with a roll or the like, is placed in a platinum pan, and a differential scanning calorimeter (DSC: The endothermic peak was measured using a Seiko Electronics Co., Ltd. RDC220-robot DSC). The endothermic peak was measured by melting the sample once, cooling it to a temperature of −50 ° C. at a rate of 10 ° C./min, and then increasing the temperature at a rate of 5 ° C./min to measure the endothermic peak.

(Measurement method of molecular weight distribution)
A gel permeation chromatography (GPC) measurement method was adopted as the molecular weight distribution measurement method in the present invention. As the method, 5 mL of orthodichlorobenzene (ODCB) is added to 5 mg of a sample (here, polypropylene resin (A), polypropylene resin (B) and polyethylene resin (C)), and the temperature is 140 ° C. for 2 hours. After dissolution by heating, the solution was filtered through a 0.5 μm filter, and the filtrate was used as a test solution. 150C ALC / GPC (manufactured by Waters) was used as the apparatus, Shodex AT-806MS 8 mmφ × 250 mm (two) was used as the column, and differential refraction was adopted as the detector. The mobile phase was the above-mentioned orthodichlorobenzene, and the conditions were set at a speed of 1.0 mL / min and a temperature of 140 ° C. As a measured value, a polystyrene conversion value was adopted.

(Measurement method of gel fraction)
The gel fraction is a calculated value. About 50 mg of a cross-linked polyolefin resin foam is accurately weighed, immersed in 25 ml of xylene at a temperature of 120 ° C. for 24 hours, filtered through a 200 mesh stainless steel wire mesh, and the wire mesh insoluble matter is vacuum dried. To do. Next, the weight of this insoluble matter was precisely weighed, and the gel fraction was calculated as a percentage according to the following formula (3).
Gel fraction (%) = {weight of insoluble matter (mg) / weight of weighed polyolefin resin foam (mg)} × 100 Formula (3)
(Apparent density measurement method)
Measured based on JIS K6767 (1999) “Foamed plastics-polyethylene test method”. Specifically, the obtained sheet-like cross-linked polyolefin resin foam was punched into a sample size of 15 cm ³ or more, the thickness and weight were measured, and the apparent density was calculated by the following formula (4).
Apparent density (kg / m ³ ) = sample weight (kg) / {sample thickness (m) × sample area (m ² )} Equation (4)
(Measurement method of tensile elongation at room temperature)
Measured based on JIS K6767 (1999) “Foamed plastics-polyethylene test method”. Specifically, the obtained sheet-like cross-linked polyolefin resin foam is punched into a dumbbell-shaped No. 1 shape and measured with a Tensilon universal testing machine UCT-500 manufactured by Orientec Co., Ltd. The difference between the length between the original mark and the length between the original marks is divided by the length between the original marks and expressed as a percentage.

(Evaluation method of tensile elongation at room temperature)
This measured value uses the following relational expression (1) as an evaluation criterion.
a> 2 * b-3 * c + 200 Formula (1)
Here, a = tensile elongation at normal temperature (%), b = apparent density (kg / m ³ ), c = gel fraction (%)
(Measurement method of tensile elongation at high temperature)
It conforms to the measurement method of “Measurement method of tensile elongation at normal temperature” described above. As a heating method, the parallel clamping type jaw part (measurement part) of the Tensilon universal testing machine is enclosed and heated in accordance with the desired temperature of the high and low temperature constant temperature bath TLF2-U2-J-F manufactured by Orientec Co., Ltd. . A sample is set and measured after preheating for 6 minutes.

(Method for evaluating heat resistance)
The value measured by the above “Method for measuring tensile elongation at high temperature” was evaluated according to the following evaluation criteria.
・ (Tensile elongation at 170 ° C .:%) / (Tensile elongation at 150 ° C .:%) ≧ 1 Formula (2)
With heat resistance ○: Satisfies the above formula (2).
No heat resistance x: The above formula (2) is not satisfied.

(Surface property evaluation method)
The surface property was evaluated by measuring the surface roughness using a surface roughness measuring device SURFCORDER SE-2300 manufactured by Kosaka Laboratory Ltd., and evaluating it according to the following criteria based on the measured value of Ra75.
Surface property (circle): Ra75 value is less than 25 micrometers.
Surface property (triangle | delta): Ra75 value is 25 micrometers or more and less than 30 micrometers.
Surface property x: Ra75 value is 30 μm or more.

(Formability evaluation method)
The obtained cross-linked polyolefin resin foams were vacuum molded, and the appearance and molding draw ratio were evaluated. Appearance is not visually swollen or wrinkled, and the molding draw ratio is a vertical cylindrical female mold with a diameter D and a depth H. When the foam is heated and straight molded using a vacuum molding machine, It is the value of H / D at the limit at which the foam can be expanded and elongated without breaking. Here, the diameter D is 50 mm. The molding drawing ratio was measured at three points where the surface temperature of the foam was 160 ° C., 180 ° C. and 200 ° C., and the value was judged according to the following evaluation criteria.
Formability: A molding drawing ratio of 0.50 or more and a good appearance at a temperature of 2 or more points.
Formability Δ: A molding drawing ratio of 0.50 or more and a good appearance at a temperature of one point.
Formability x: No temperature at which the forming ratio is 0.50 or more, or poor appearance.

(Comprehensive evaluation)
From the evaluation results in the above “heat resistance evaluation method”, “surface property evaluation method”, and “formability evaluation method”, comprehensive evaluation was performed according to the following evaluation criteria.
Overall evaluation ○: When all evaluations are marked with ○.
Comprehensive evaluation (triangle | delta): When (circle) evaluation is two or less and there is no x evaluation.
Comprehensive evaluation x: When there are one or more x mark evaluations.

  In each evaluation result, ◯ is excellent, Δ is good, and x is bad.

Example 1
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 40% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 40% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 8 parts of azodicarbonamide as a foaming agent, 5 parts of divinylbenzene as a crosslinking aid, and a mixture obtained by mixing with a Henschel mixer The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 100 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.1 mm, an apparent density of 67 kg / m ³ and a gel fraction of 56%. .

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 180%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. The tensile elongation at a temperature of 150 ° C. was 200%, and the tensile elongation at a temperature of 170 ° C. was 220%. The surface roughness Ra75 value was 20 μm.

(Example 2)
Polypropylene resin (A) (homopolypropylene: MFR = 0.9 g / 10 min, DSC peak temperature 167 ° C., Mw = 560,000) 30% by weight and polypropylene resin (B) (ethylene-propylene random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 40% by weight, polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min, density 0.932 g) / Cm ³ , Mw = 60,000) 30% by weight, 9 parts of azodicarbonamide as a blowing agent, 5 parts of divinylbenzene as a crosslinking aid, and a mixture obtained by mixing with a Henschel mixer, 60 mmφ uniaxial with vent The sheet was extruded with an extruder and formed into a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with a 150 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 1.9 mm, an apparent density of 70 kg / m ³ and a gel fraction of 54%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 190%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed with a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 190%, and the tensile elongation at a temperature of 170 ° C. was 210%. The surface roughness Ra75 value was 19 μm.

(Example 3)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 50% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 30% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 6 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were mixed with a Henschel mixer. The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 110 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 1.6 mm, an apparent density of 85 kg / m ³ , and a fraction of 54%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 240%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at temperatures of 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 210%, and the tensile elongation at a temperature of 170 ° C. was 260%. Further, the surface roughness Ra75 value was 17 μm.

Example 4
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.7 g / 10 min, DSC peak temperature 162 ° C., Mw = 420,000) 40% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 40% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 7 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were mixed with a Henschel mixer. The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 90 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.0 mm, an apparent density of 67 kg / m ³ and a gel fraction of 50%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at ordinary temperature was measured and found to be 250%. Further, the obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 210%, and the tensile elongation at a temperature of 170 ° C. was 260%. Further, the surface roughness Ra75 value was 17 μm.

(Example 5)
Polypropylene resin (A) (homopolypropylene: MFR = 0.5 g / 10 min, DSC peak temperature 165 ° C., Mw = 860,000) 40% by weight and polypropylene resin (B) (ethylene-propylene random copolymer: MFR = 2.2 g / 10 min, DSC peak temperature 138 ° C., Mw = 830000) 40% by weight, polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm) ³ , Mw = 60,000) 20% by weight, 6 parts of azodicarbonamide as a blowing agent, 5 parts of divinylbenzene as a crosslinking aid, and a mixture obtained by mixing with a Henschel mixer, a 60 mmφ single screw extruder with a vent And extruded to form a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with an electron beam of 120 kGy using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 1.7 mm, an apparent density of 72 kg / m ³ and a gel fraction of 52%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 220%. Further, the obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, the molding drawing ratio was measured, and it was 0.50 or more at all temperatures of 160, 180 ° C. and 200 ° C. The tensile elongation at a temperature of 150 ° C. was 210%, and the tensile elongation at a temperature of 170 ° C. was 230%. Further, the surface roughness Ra75 value was 22 μm.

(Example 6)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 50% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 25% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000 **) 25% by weight, 10 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were obtained by mixing with a Henschel mixer. The resin mixture was extruded with a vented 60 mmφ single screw extruder and formed into a 1 mm thick sheet.

The sheet thus obtained was irradiated with a 100 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.0 mm, an apparent density of 53 kg / m ³ and a gel fraction of 52%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 190%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed with a differential scanning calorimeter. Further, when the molding drawing ratio was measured, only the temperature of 200 ° C. was a value of 0.50 or more. The tensile elongation at a temperature of 150 ° C. was 200%, and the tensile elongation at a temperature of 170 ° C. was 220%. Further, the surface roughness Ra75 value was 21 μm.

(Example 7)
Polypropylene resin (A) (homopolypropylene: MFR = 2.2 g / 10 min, DSC peak temperature 166 ° C., Mw = 350,000) 40% by weight and polypropylene resin (B) (ethylene-propylene random copolymer: MFR = 2.2 g / 10 min, DSC peak temperature 138 ° C., Mw = 830000) 40% by weight, polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm) ³ , Mw = 60,000) 20% by weight, 12 parts of azodicarbonamide as a blowing agent, 5 parts of divinylbenzene as a crosslinking aid, and a mixture obtained by mixing with a Henschel mixer, a 60 mmφ single screw extruder with a vent And extruded to form a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with a 100 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.2 mm, an apparent density of 49 kg / m ³ and a gel fraction of 51%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 220%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at a temperature of 180 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 210%, and the tensile elongation at a temperature of 170 ° C. was 220%. The surface roughness Ra75 value was 23 μm.

(Example 8)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 0.35 g / 10 min, DSC peak temperature 165 ° C., Mw = 1050,000) 40% by weight, polypropylene resin (B) (ethylene -Propylene random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., 40% by weight Mw = 1,100,000 and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g) / 10 min, density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 8 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were obtained by mixing with a Henschel mixer. The mixture was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with an 80 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.3 mm, an apparent density of 61 kg / m ³ and a gel fraction of 52%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 200%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 220%, and the tensile elongation at a temperature of 170 ° C. was 240%. The surface roughness Ra75 value was 25 μm.

  The results of Examples 1-8 are summarized in Table 1.

  The cross-linked polyolefin resin foam obtained in Example 1 was subjected to corona discharge treatment, applied with a two-component urethane adhesive, and then laminated with a polyvinyl chloride sheet (0.5 mm) to obtain a laminate. This was molded by a low pressure injection molding method (thermoplastic resin: homopolypropylene, MFR = 20 g / min, resin temperature 180 ° C.) to obtain a molded article having a beautiful appearance.

(Comparative Example 1)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 60% by weight, polyethylene resin (C) (linear low Density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm ³ , Mw = 60,000) 40 wt%, 8 parts of azodicarbonamide as a foaming agent, 5 parts of divinylbenzene as a crosslinking aid, Henschel mixer The mixture obtained by mixing was extruded with a vented 60 mmφ single screw extruder and formed into a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with an electron beam of 125 kGy using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.1 mm, an apparent density of 67 kg / m ³ and a gel fraction of 56%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 160%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, the molding drawing ratio was measured and found to be 0.50 or less at all temperatures of 160 ° C., 180 ° C. and 200 ° C. The tensile elongation at a temperature of 150 ° C. was 180%, and the tensile elongation at a temperature of 170 ° C. was 210%. The surface roughness Ra75 value was 19 μm.

(Comparative Example 2)
Polypropylene resin (A) (homopolypropylene: MFR = 2.2 g / 10 min, DSC peak temperature 166 ° C., Mw = 350,000) 60% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm ³ , Mw = 60,000) 40% by weight, 8 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid can be mixed with a Henschel mixer. The obtained mixture was extruded with a vented 60 mmφ single screw extruder and formed into a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with an electron beam of 133 kGy using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.1 mm, an apparent density of 63 kg / m ³ and a gel fraction of 58%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 140%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed with a differential scanning calorimeter. Further, the molding drawing ratio was measured and found to be 0.50 or less at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 180%, and the tensile elongation at a temperature of 170 ° C. was 200%. The surface roughness Ra75 value was 18 μm.

(Comparative Example 3)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 60% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000) 40% by weight, 8 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid Attempts were made to extrude the mixture obtained by mixing with a Henschel mixer with a vented 60 mmφ single screw extruder, but the foaming agent was decomposed and the surface condition was not good, so irradiation and foaming were stopped.

(Comparative Example 4)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 25% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 25% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 50% by weight, 10 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were mixed with a Henschel mixer. The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 110 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.1 mm, an apparent density of 61 kg / m ³ and a gel fraction of 54%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at ordinary temperature was measured and found to be 210%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 260%, and the tensile elongation at a temperature of 170 ° C. was 240%. The surface roughness Ra75 value was 19 μm.

(Comparative Example 5)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 60% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: 20% by weight of MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000) and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 9 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were mixed with a Henschel mixer. The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 110 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.0 mm, an apparent density of 66 kg / m ³ and a gel fraction of 54%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 150%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, the molding drawing ratio was measured and found to be 0.50 or less at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 190%, and the tensile elongation at a temperature of 170 ° C. was 200%. Further, the surface roughness Ra75 value was 17 μm.

(Comparative Example 6)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 20% by weight, polypropylene resin (B) (ethylene-propylene Random copolymer: MFR = 0.8 g / 10 min, DSC peak temperature 148 ° C., Mw = 1,100,000 60% by weight and polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min) , Density 0.932 g / cm ³ , Mw = 60,000) 20% by weight, 9 parts of azodicarbonamide as a foaming agent, and 5 parts of divinylbenzene as a crosslinking aid were mixed with a Henschel mixer. The sheet was extruded into a 1 mm thick sheet by a 60 mmφ single screw extruder with a vent.

The sheet thus obtained was irradiated with a 110 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.2 mm, an apparent density of 65 kg / m ³ and a gel fraction of 54%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 220%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed by a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 230%, and the tensile elongation at a temperature of 170 ° C. was 200%. Further, the surface roughness Ra75 value was 17 μm.

(Comparative Example 7)
Polypropylene resin (A) (ethylene-propylene block copolymer: MFR = 1.3 g / 10 min, DSC peak temperature 164 ° C., Mw = 470,000) 40% by weight, polypropylene resin (B) (homopolypropylene: MFR = 0.9 g / 10 min, DSC peak temperature 167 ° C., Mw = 560,000) 40% by weight, polyethylene resin (C) (linear low density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm) ³ , Mw = 60,000) 20% by weight, 12 parts of azodicarbonamide as a blowing agent, 5 parts of divinylbenzene as a crosslinking aid, and a mixture obtained by mixing with a Henschel mixer, a 60 mmφ single screw extruder with a vent Attempted to form an extruded sheet with a foam, but the foaming agent decomposed and the surface condition was not good Was discontinued because the irradiation-foaming.

(Comparative Example 8)
Polypropylene resin (B) (ethylene-propylene random copolymer: MFR = 2.2 g / 10 min, DSC peak temperature 138 ° C., Mw = 830000) 80% by weight, polyethylene resin (C) (linear low Density polyethylene: MFR = 12 g / 10 min, density 0.932 g / cm ³ , Mw = 60,000) 50 wt%, 10 parts of azodicarbonamide as a foaming agent, 5 parts of divinylbenzene as a crosslinking aid, Henschel mixer The mixture obtained by mixing was extruded with a vented 60 mmφ single screw extruder and formed into a sheet having a thickness of 1 mm.

The sheet thus obtained was irradiated with a 110 kGy electron beam using an electron beam irradiator to crosslink the resin. This was immersed in a salt bath heated to a temperature of 240 ° C. to obtain a crosslinked polyolefin resin foam having a thickness of 2.1 mm, an apparent density of 61 kg / m ³ and a gel fraction of 52%.

  With respect to the obtained crosslinked polyolefin resin foam, the tensile elongation at room temperature was measured and found to be 280%. The obtained crosslinked polyolefin resin foam was pressed with a mixing roll to crush bubbles, and the endothermic peak temperature was confirmed with a differential scanning calorimeter. Further, when the molding drawing ratio was measured, it was a value of 0.50 or more at all temperatures of 160 ° C., 180 ° C. and 200 ° C. Further, the tensile elongation at a temperature of 150 ° C. was 310%, and the tensile elongation at a temperature of 170 ° C. was 220%. The surface roughness Ra75 value was 20 μm.

  The results of Comparative Examples 1-8 are summarized in Table 2.

  The crosslinked polyolefin resin foam obtained in the present invention is expected to have an effect of reducing the defect rate by exhibiting excellent heat resistance against processing during molding, for example, heating in low-pressure injection molding. The crosslinked polyolefin resin foam of the present invention is excellent in flexibility, light weight, and heat insulation, and is suitably used as an interior material for vehicles such as a ceiling, a door, and an instrument panel.

Claims (8)

20 to 50% by weight of a polypropylene resin (A) having an endothermic peak of 160 ° C. or higher by a differential scanning calorimeter and 20 to 50% by weight of a polypropylene resin (B) having an endothermic peak by a differential scanning calorimeter of less than 160 ° C. % And a polyolefin resin composition containing 20 to 40% by weight of a polyethylene resin (C), a crosslinked polyolefin resin foam. The crosslinked polyolefin resin foam according to claim 1, wherein the polypropylene resin (A) is an ethylene-propylene block copolymer. The crosslinked polyolefin resin foam according to claim 1, wherein the polypropylene resin (A) is homopolypropylene. The crosslinked polyolefin resin foam according to claim 1, wherein the polypropylene resin (A) is an ethylene-propylene random copolymer. The melt flow rate of the polypropylene resin (A) is 0.4 to 1.8 g / 10 min, and the weight ratio of the polypropylene resin (A) to the polypropylene resin (B) is 1: 0.5 to 1. The cross-linked polyolefin resin foam according to claim 1, which is 1.5. A laminate obtained by bonding another material to the crosslinked polyolefin resin foam according to claim 1. A molded article obtained by molding the crosslinked polyolefin resin foam according to claim 1 or the laminate according to claim 6. An automobile interior material using any one of the crosslinked polyolefin resin foam according to claim 1, the laminate according to claim 6, or the molded article according to claim 7.

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